In a conventional turbine compressor component, rotor blades are held in a rotating blade wheel by means of a dovetail connection (i.e., a dovetail on the blade is received in a complimentary slot in the wheel).
The fit between the blade and the dovetail slot in the wheel is loose to allow for assembly and tolerances. Therefore, if the blades are not properly retained, the loose fit may allow the hardware to move in the slot, leading to excessive wear. The excessive wear would eventually fail the part, requiring the unit to be shut down until a repair can be made.
Typically, each blade is retained in the wheel to limit motion along the wheel dovetail slot by one or more stakes. This is a process where material at the edge of the wheel slot is plastically deformed and displaced into a void created by a local chamfer of the blade dovetail. This is a manual and highly variable process which can in some cases provide inadequate retention of the blade in the wheel. Vibratory forces acting on the rotor can produce wear on the stake leading to eventual failure of the retention feature. Once the stake is worn, the blade can then slide freely in the dovetail slot. At very high amplitudes, this motion can lead to wearing of the blade dovetail and eventual failure. This could then lead to blade liberation and subsequent collateral damage to the gas turbine. There have also been many documented instances of rotor blades being installed incorrectly either by inserting the blade in the dovetail slot backwards or inserting the blade in the wrong axial position (stage). Some of these mis-assemblies have been identified as causes of subsequent failure of machine equipment.
There remains a need for a field-retrofittable blade retention mechanism that will allow the blade to be installed, removed and reinstalled without damaging the blades of the wheel.